A recently introduced drug, 2-[4-(2-furoyl)-1-piperazine-1-yl]-4-amino-6,7-dimethoxyquinazoline, commonly identified by the generic name prazosin, is a hypotensive drug producing peripheral arterial dilation. This drug is represented by the formula: ##STR1## This drug however, as reported in The Lancet, May 10, 1975, at page 1095, exhibits significant toxicity and can cause a profound fall in blood pressure. Sudden collapse with loss of consciousness for periods ranging from a few minutes to one hour following use of this drug have been reported. (The Lancet and British Medical Journal, June 28, 1975, pages 727, 728). The drug prazosin also has a very low solubility and it is therefore postulated that the problem of toxicity sometimes resulting upon oral administration of this drug may be caused by erratic absorption.